The invention relates to a polyimide molded body, particularly a polyimide membrane, which has been functionalized by a chemical group and to a method for the manufacture thereof.
Polyimides of different chemical compositions have been known and have been commercially available for a long time. Various molded bodies can be formed from such polyimides by casting. An important application field for polyimides resides for example in the manufacture of injection-molded bodies and of membranes.
Different types of polyimides can easily be formed into membranes with different separation properties by means of a phase inversion process. A method for the manufacture of integral symmetrical polyetherimide membranes is for example described in DE-A 34 20 373. These known membranes can be for example coated with polydimethylsiloxane and used for the separation of gases.
Another polyimide membrane and a method for the manufacture thereof are described in DE-A 37 16 916. This membrane is preferably used for the ultrafiltration and, as coated carrier membrane, for the manufacture of composite membranes.
Polyimides are generally relatively hydrophobic polymers, which cannot be easily wetted by water. The filtration of aqueous solutions leads to wetting problems and may result in a non-specific adsorption of compounds in the solution (fouling) which causes a substantial reduction in the membrane efficiency. U.S. Pat. No. 4,798,847 discloses a process for the manufacture of polyimide membranes, wherein a hydrophilic compound is added to the hydrophobic base polymer, particularly polyvinyl pyrolidon, which is cross-linked and in this way fixed to the membrane and which remains therefore at least partially in the finished membrane. Such hydrophilically modified polyimide membranes are suitable for ultra and/or micro-filtration.
However, polyimide membranes generally do not include any active functional groups as for example aminhydroxyl, carboxyl, aldehyde and other reactive groups do. As a result, these known polyimide membranes are not suitable for the manufacture of affinity membranes. Polyimides include generally components, which can be functionalized. The chemical conversions required for the introduction of functionalized groups however are time-consuming and cannot be performed continuously or are difficult to be performed continuously or they present health hazards or they damage functionalized membranes.
However, DE-A 41 17 501 discloses the use of an amino-modified polyimide membrane, which can be used for gas separation and for ultra-filtration processes. The manufacture of this membrane is based on a homogeneous polyimide solution, into which an organic multifunctional compound with at least two primary amino groups per molecule are introduced in a concentration of 0.05 to 5% of the reaction mixture and which is dissolved therein. This mixture of substances is then left to react for 1 hour to 10 days, wherein, with the practically complete consumption of the amino groups of the organic multi-functional compounds, the polyamide macro-molecules are branched and cross-linked such that the viscosity of the polyimide solution is increased. However, it has been found that the amount of modifying amino compounds in the homogeneous solution must be very accurately controlled, that is, depending on the amino-compound utilized, it must be relatively small in order to obtain soluble polymer solutions. With an overdose, the homogeneous solution forms an insoluble gel. This membrane forming polymer solution is suitable for forming membranes also from diluted polymer solutions without this solution penetrating a textile support structure. Since the amino-containing modifications react while consuming all amino-functions, the content of free amino-groups at the surface of the membrane formed is very low, that is practically zero, so that the membrane in this form, that is, with the use of the rest amino groups possibly present, is not suitable.
It is the object of the present invention, to provide a functionalized polyimide molded body, and particularly a functionalized polyimide membrane, which can be functionalized in a controlled manner and which has a high functionalization degree. It is further an object of the invention to provide a method for the manufacture of such a polyimide molded body or such a polyimide membrane, wherein this functionalization occurs in a simple and economic manner in an aqueous medium.